1. Field of the Invention
Embodiments of the present invention generally relate to an earth removal member with features for facilitating subsequent drill-through.
2. Description of the Related Art
The drilling of wellbores for oil and gas production conventionally employs strings of drill pipe to which, at one end, is secured a drill bit. After a selected portion of the wellbore has been drilled, the wellbore is usually cased with a string of casing or lined with a string of liner. Drilling and casing/lining according to the conventional process typically requires sequentially drilling the wellbore using drill string with a drill bit attached thereto, removing the drill string and drill bit from the wellbore, and disposing casing/lining into the wellbore. Further, often after a section of the borehole cased/lined, which is usually cemented into place, additional drilling beyond the end of the casing/liner may be desired.
Unfortunately, sequential drilling and casing may be time consuming because, as may be appreciated, at the considerable depths reached during oil and gas production, the time required to retrieve the drill string may be considerable. Thus, such operations may be costly as well due to the high cost of rig time. Moreover, control of the well may be difficult during the period of time that the drill pipe is being removed and the casing/lining is being disposed into the borehole.
Some approaches have been developed to address the difficulties associated with conventional drilling and casing/lining operations. Of initial interest is an apparatus which is known as a reaming casing shoe that has been used in conventional drilling operations. Reaming casing shoes have become available relatively recently and are devices that are able to drill through modest obstructions within a borehole that has been previously drilled. In addition, the reaming casing shoe may include an inner section manufactured from a material which is drillable by drill bits. Accordingly, when cemented into place, the reaming casing shoe usually poses no difficulty to a subsequent drill bit.
As a further extension of the reaming casing shoe concept, in order to address the problems with sequential drilling and casing, drilling with casing/liner is gaining popularity as a method for drilling a wellbore, wherein the casing/liner is used as the drill string and, after drilling, the casing/liner remains downhole to line the wellbore. Drilling with casing/liner employs a drill bit attached to the casing/liner string, so that the drill bit functions not only to drill the earth formation, but also to guide the casing/liner into the wellbore. This may be advantageous as the casing/liner is disposed into the wellbore as it is formed by the drill bit, and therefore eliminates the necessity of retrieving the drill string and drill bit after reaching a target depth where cementing is desired.
While this procedure greatly increases the efficiency of the drilling procedure, a further problem is encountered when the casing/liner is cemented upon reaching the desired depth. While one advantage of drilling with casing is that the drill bit does not have to be retrieved from the wellbore, further drilling may be required. Thus, further drilling must pass through the drill bit attached to the end of the casing/liner.
However, drilling through the casing/liner drill bit may be difficult as drill bits are required to remove rock from formations and accordingly often include very drilling resistant, robust structures typically manufactured from hard or super-hard materials. Attempting to drill through a drill bit affixed to the end of a casing/liner may result in damage to the subsequent drill bit and bottom-hole assembly deployed or possibly the casing/liner itself. It may be possible to drill through a drill bit or a casing with special tools known as mills, but these tools are unable to penetrate rock formations effectively and the mill would have to be retrieved or “tripped” from the wellbore and replaced with a drill bit. In this case, the time and expense saved by drilling with casing would be mitigated or even lost.